In order to allow re-use of parameters across multiple commands, remove them

from any commands that are created prior to calling Dispose (as that is not
sufficient). This will allow use cases where queries are retried (using Polly)
for instance, and the parameters are being passed via IDynamicParameters
or ICustomQueryParameter

Author: James Crowley

Dapper.Tests/ParameterTests.cs

@@ -21,7 +21,7 @@ namespace Dapper.Tests
 {
     public class ParameterTests : TestBase
     {
-        public class DbParams : SqlMapper.IDynamicParameters, IEnumerable<IDbDataParameter>
+        public class DbDynamicParams : SqlMapper.IDynamicParameters, IEnumerable<IDbDataParameter>
         {
             private readonly List<IDbDataParameter> parameters = new List<IDbDataParameter>();
             public IEnumerator<IDbDataParameter> GetEnumerator() { return parameters.GetEnumerator(); }
@@ -37,6 +37,21 @@ void SqlMapper.IDynamicParameters.AddParameters(IDbCommand command, SqlMapper.Id
                     command.Parameters.Add(parameter);
             }
         }
+        
+        public class DbCustomParam : SqlMapper.ICustomQueryParameter
+        {
+            private readonly IDbDataParameter _sqlParameter;
+
+            public DbCustomParam(IDbDataParameter sqlParameter)
+            {
+                _sqlParameter = sqlParameter;
+            }
+
+            public void AddParameter(IDbCommand command, string name)
+            {
+                command.Parameters.Add(_sqlParameter);
+            }
+        }
 
         private static List<Microsoft.SqlServer.Server.SqlDataRecord> CreateSqlDataRecordList(IEnumerable<int> numbers)
         {
@@ -672,9 +687,9 @@ public class HazSqlHierarchy
 #endif
 
         [Fact]
-        public void TestCustomParameters()
+        public void TestDynamicParameters()
         {
-            var args = new DbParams {
+            var args = new DbDynamicParams {
                 new SqlParameter("foo", 123),
                 new SqlParameter("bar", "abc")
             };
@@ -684,7 +699,53 @@ public void TestCustomParameters()
             Assert.Equal(123, foo);
             Assert.Equal("abc", bar);
         }
+        
+        [Fact]
+        public void TestDynamicParametersReuse()
+        {
+            var args = new DbDynamicParams {
+                new SqlParameter("foo", 123),
+                new SqlParameter("bar", "abc")
+            };
+            var result1 = connection.Query("select Foo=@foo, Bar=@bar", args).Single();
+            var result2 = connection.Query("select Foo=@foo, Bar=@bar", args).Single();
+            Assert.Equal(123, result1.Foo);
+            Assert.Equal("abc", result1.Bar);
+            Assert.Equal(123, result2.Foo);
+            Assert.Equal("abc", result2.Bar);
+        }
 
+        
+        [Fact]
+        public void TestCustomParameter()
+        {
+            var args = new {
+                foo = new DbCustomParam(new SqlParameter("foo", 123)),
+                bar = "abc"
+            };
+            var result = connection.Query("select Foo=@foo, Bar=@bar", args).Single();
+            int foo = result.Foo;
+            string bar = result.Bar;
+            Assert.Equal(123, foo);
+            Assert.Equal("abc", bar);
+        }
+        
+        [Fact]
+        public void TestCustomParameterReuse()
+        {
+            var args = new {
+                foo = new DbCustomParam(new SqlParameter("foo", 123)),
+                bar = "abc"
+            };
+            var result1 = connection.Query("select Foo=@foo, Bar=@bar", args).Single();
+            var result2 = connection.Query("select Foo=@foo, Bar=@bar", args).Single();
+            Assert.Equal(123, result1.Foo);
+            Assert.Equal("abc", result1.Bar);
+            Assert.Equal(123, result2.Foo);
+            Assert.Equal("abc", result2.Bar);
+        }
+        
+        
         [Fact]
         public void TestDynamicParamNullSupport()
         {

Dapper/SqlMapper.cs

@@ -1040,6 +1040,8 @@ private static GridReader QueryMultipleImpl(this IDbConnection cnn, ref CommandD
                     }
                     reader.Dispose();
                 }
+
+                cmd?.Parameters.Clear();
                 cmd?.Dispose();
                 if (wasClosed) cnn.Close();
                 throw;
@@ -1127,6 +1129,8 @@ private static IEnumerable<T> QueryImpl<T>(this IDbConnection cnn, CommandDefini
                     reader.Dispose();
                 }
                 if (wasClosed) cnn.Close();
+                
+                cmd?.Parameters.Clear();
                 cmd?.Dispose();
             }
         }
@@ -1234,6 +1238,7 @@ private static T QueryRowImpl<T>(IDbConnection cnn, Row row, ref CommandDefiniti
                     reader.Dispose();
                 }
                 if (wasClosed) cnn.Close();
+                cmd?.Parameters.Clear();
                 cmd?.Dispose();
             }
         }
@@ -1458,6 +1463,7 @@ private static IEnumerable<TReturn> MultiMapImpl<TFirst, TSecond, TThird, TFourt
                 }
                 finally
                 {
+                    ownedCommand?.Parameters.Clear();
                     ownedCommand?.Dispose();
                     if (wasClosed) cnn.Close();
                 }
@@ -1528,6 +1534,7 @@ private static IEnumerable<TReturn> MultiMapImpl<TReturn>(this IDbConnection cnn
                 }
                 finally
                 {
+                    ownedCommand?.Parameters.Clear();
                     ownedCommand?.Dispose();
                     if (wasClosed) cnn.Close();
                 }
@@ -2831,6 +2838,7 @@ private static int ExecuteCommand(IDbConnection cnn, ref CommandDefinition comma
             finally
             {
                 if (wasClosed) cnn.Close();
+                cmd?.Parameters.Clear();
                 cmd?.Dispose();
             }
         }
@@ -2858,6 +2866,7 @@ private static T ExecuteScalarImpl<T>(IDbConnection cnn, ref CommandDefinition c
             finally
             {
                 if (wasClosed) cnn.Close();
+                cmd?.Parameters.Clear();
                 cmd?.Dispose();
             }
             return Parse<T>(result);
@@ -2881,7 +2890,11 @@ private static IDataReader ExecuteReaderImpl(IDbConnection cnn, ref CommandDefin
             finally
             {
                 if (wasClosed) cnn.Close();
-                if (cmd != null && disposeCommand) cmd.Dispose();
+                if (cmd != null && disposeCommand)
+                {
+                    cmd.Parameters.Clear();
+                    cmd.Dispose();
+                }
             }
         }